Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$166.48	3.627%	$172.5182	$172.52	$172.50	$172.50
Purchase #2	$91.35	9.383%	$99.9214	$99.92	$99.90	$99.90
Purchase #3	$192.93	7.132%	$206.6898	$206.69	$206.70	$206.70
Purchase #4	$202.87	4.682%	$212.3684	$212.37	$212.35	$212.40
Purchase #5	$87.87	12.790%	$99.1086	$99.11	$99.10	$99.10
Purchase #6	$207.97	11.132%	$231.1212	$231.12	$231.10	$231.10
Purchase #7	$247.36	9.490%	$270.8345	$270.83	$270.85	$270.80
7 purchase totals =	$1,196.83		$1,292.5621	$1,292.56	$1,292.50	$1,292.50